Fabrication of capacitors and recovery of capacitor fabrication materials

ABSTRACT

Fabricating a capacitor include using a first etching solution to etch a first sheet of material so as to generate a spent etchant. At least one chemical component is recovered from the spent etchant. A second etching solution is used to etch a second sheet of material. The second etchant includes at least one of the chemical components that was recovered from the spent etchant.

RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.16/785,594, filed on Feb. 8, 2020, and incorporated herein in itsentirety; and U.S. patent application Ser. No. 16/785,594 claims thebenefit of U.S. Patent application Ser. No. 62/804,055, filed on Feb.11, 2019, and incorporated herein in its entirety and U.S. patentapplication Ser. No. 16/785,594 also claims the benefit of U.S. Patentapplication Ser. No. 62/804,060, filed on Feb. 11, 2019, andincorporated herein in its entirety.

FIELD

The invention relates to electrochemical devices. In particular, theinvention relates to capacitors.

BACKGROUND

Electrodes for capacitors are often fabricated by etching tunnels in asheet of material that includes an anode metal. An oxide of the anodemetal is then formed on the exposed anode metal. In order to preventclogging of the tunnels by the oxide, the tunnels are generally widenedbefore the oxide is formed in the tunnels. After the formation of theoxide, the sheet of material generally becomes brittle. The electrode isremoved from the sheet of material using mechanical cutting techniquesor other cutting techniques such as laser cutting.

During fabrication of the capacitor, one or more electrical conductorsare generally connected to the electrode in order to provide electricalcommunication between the electrode and a terminal of the capacitor.Welding is often used to make this connection, however, welding ishampered by the composite nature of the electrode. In order to overcomethis problem, the welded region of the electrode is masked during theetching of the tunnels and during the formation of the oxide. Thismasking prevents the tunnels from being formed under the mask. As aresult, the final electrode includes an inactive region where the sheetof material excludes the tunnels. In some instances, the inactive regionalso excludes the oxide. An electrical conductor is then connected tothe inactive region of the electrode.

While masking the welded region solves the problem of welding theelectrode, it has the unwanted side effect of contributing to mechanicalwaviness across the surface of the electrode formation of the oxide. Thewaviness can be caused by etching and/or oxide formation reducing thesize of the unmasked portion of the electrode and producing a strain inregions of the electrode where an etched region is interfaced with aninactive region. As a result, there is a need for improved capacitorelectrode construction.

Additionally, etching the tunnels in the anode of a capacitor can bedone with processes such as electrochemical etching or electrochemicaldrilling. In electrochemical etching and/or electrochemical drilling, asheet of a material is at least partially immersed in a bath of etchingsolution. In some instances, the etching solution includes one or moreacids and sodium perchlorate.

The etching process leaves material from the sheet of material dissolvedin spent etching solution. For instance, when the sheet of material isaluminum, the etching process results dissolved aluminum being presentin the spent etching solution. However, high levels of dissolvedaluminum causes tunnel initiation to drop and the pH of the bath toincrease. As a result, fresh etching solution is added to the etch bathto control pH and aluminum concentration. The spent etching solutioncannot be discharged to POTW (Publicly Owned Treatment Work) andaccordingly requires costly waste disposal. Additionally, sodiumperchlorate is expensive and, highly stable thermally, and does notbreak down quickly in the environment. As a result, there is a need torecover spent one or more compounds from spent etching solution.

SUMMARY

A capacitor includes an electrode with a first active region thatincludes tunnels extending into an electrode metal. The electrode alsohas a first inactive region that includes the electrode metal but doesnot include the tunnels extending into the electrode metal. The firstinactive region has a first shape that includes multiple firstprojections that each projects from a perimeter of a first semicircle.

In some instances, the electrode has a second inactive region thatincludes the electrode metal but does not include the tunnels extendinginto the electrode metal. The second inactive region has a second shapethat includes multiple second projections that each projects from aperimeter of a second semicircle. A first side of the electrode isopposite from a second side of the electrode. The first active regionand the first inactive region are on the first side of the electrode andthe second active region and the second inactive region are on thesecond side of the electrode. The first semicircle can be aligned withthe second semicircle in that a first line can extend through the centerof the first semicircle and also through the center of the secondsemicircle with the first line being parallel to a second line that isperpendicular to the first side of the sheet of material.

A capacitor electrode precursor includes a sheet of material that has afirst active region that includes tunnels extending into an electrodemetal. The sheet of material also has a first inactive region thatincludes the electrode metal but does not include the tunnels extendinginto the electrode metal. The first inactive region has a first shapethat includes multiple first projections that each projects from aperimeter of a first circle.

In some instances, the sheet of material includes a second active regionthat includes tunnels extending into the electrode metal. The sheet ofmaterial also has a second inactive region that includes the electrodemetal but does not include the tunnels extending into the electrodemetal. The second inactive region has a second shape that includesmultiple second projections that each projects from a perimeter of asecond circle. The first side of the sheet of material is opposite fromthe second side of the sheet of material. The first active region andthe first inactive region are on the first side of the sheet of materialand the second active region and the second inactive region are on thesecond side of the sheet of material. The first circle can be alignedwith the second circle in that a first line can extend through thecenter of the first circle and also through the center of the secondcircle with the first line being parallel to a second line that isperpendicular to the first side of the sheet of material.

In some instances, a capacitor is fabricated by generating a sheet ofmaterial that has a first active region that includes tunnels extendinginto an electrode metal. The sheet of material has a first inactiveregion that includes the electrode metal but does not include thetunnels extending into the electrode metal. The first inactive regionhas a first shape that includes multiple first projections that eachprojects from a perimeter of a circle. An electrode is removed from thesheet of material such that the electrode includes a portion of theinactive region that has one or more of the projections that eachextends from a semicircle. The semicircle is a portion of the circle.

In one embodiment, fabricating a capacitor includes using a firstetching solution to etch a first sheet of material so as to generate aspent etchant. At least one chemical component is recovered from thespent etchant. A second etching solution is sued to etch a second sheetof material. The second etchant includes at least one of the chemicalcomponents that was recovered from the spent etchant.

Recovering one or more chemical components from an etching solution usedin capacitor fabrication includes exposing a sheet of material to anetching solution so as to generate a spent etching solution thatincludes metal ions from the sheet of material. The method also includesadding a precipitant to the spent etching solution so as to causeprecipitation of a compound in a precipitation solution. The compoundincludes the metal ions from the sheet of material. Additionally, theprecipitant is disassociated in the precipitation solution such that theprecipitation solution includes cations from the precipitant. The methodalso includes removing from the precipitation solution at least aportion of the cations from the precipitant.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A through FIG. 1H illustrate the construction of a capacitor. FIG.1A is a sideview of an anode that is suitable for use in the capacitor.

FIG. 1B is a cross-section of the anode shown in FIG. 1A taken along theline labeled B in FIG. 1A.

FIG. 1C is a cross-section of the anode shown in FIG. 1A taken along theline labeled B in FIG. 1A.

FIG. 1D is a sideview of a cathode that is suitable for use in thecapacitor.

FIG. 1E is a cross-section of the cathode shown in FIG. 1D taken alongthe line labeled D in FIG. 1D.

FIG. 1F is a cross section of an electrode assembly where anodes arealternated with cathodes. The anodes and cathodes can be constructedaccording to FIG. 1A through FIG. 1E.

FIG. 1G is a schematic diagram of a capacitor that includes theelectrode assembly of FIG. 1F positioned in a capacitor case.

FIG. 1H is a sideview of an interface between an anode and a cathodethat are adjacent to one another in the capacitor of FIG. 1G.

FIG. 2A through FIG. 2H illustrate a method of generating an anode foruse in a capacitor constructed according to FIG. 1A through FIG. 1H.FIG. 2A is a topview of a sheet of material from which the anode isconstructed. The sheet of material can be a sheet of an anode metal.

FIG. 2B is a portion of a cross section of the sheet of material showingan interface between the side of the sheet of material and theatmosphere in which the sheet of material is positioned.

FIG. 2C illustrates the sheet of material of FIG. 2B after the formationof preliminary channels in the sheet of material.

FIG. 2D illustrates the sheet of material of FIG. 2C after widening thepreliminary channels.

FIG. 2E illustrates the sheet of material of FIG. 2C after formation ofan anode metal oxide on the exposed surfaces of an anode metal.

FIG. 2F illustrates an example of a compression mechanism for performinga thermal compression operation on the sheet of material.

FIG. 2G illustrate an anode extracted from the sheet of material shownin FIG. 2F.

FIG. 2H illustrates a capacitor that includes the anode of FIG. 2G.

FIG. 3 is a cross section of a portion of a sheet of material showingmasks that are aligned with one another on opposing sides of the sheetof material.

FIG. 4A through FIG. 4D illustrate a first mask and a second masksuitable for use with a sheet of material from which an electrode isconstructed. FIG. 4A is a topview of the first mask.

FIG. 4B is a bottomview of the second mask.

FIG. 4C is a topview of the portion of the sheet of material thatincludes the first mask aligned with the second mask. In FIG. 4C, thefirst mask and the sheet of material are treated as transparent. As aresult, the features underlying the first mask are evident in FIG. 4C.

FIG. 4D is a magnified view of an edge of the first mask and the secondmask arranged as shown in FIG. 4C.

FIG. 4E is a magnified view of a first mask and a second mask of FIG. 4Athrough FIG. 4D. The first mask and the second mask of FIG. 4E are notaligned but have the same angular orientation as shown in FIG. 4C andFIG. 4D.

FIG. 4F illustrates a portion of a first side of the sheet of materialof FIG. 4C and the corresponding portion from the second side of thesheet of material. The first mask and the second mask have been removedfrom the sheet of material exposing an inactive region on the first sideand on the second side of the sheet of material.

FIG. 4G shows the first side and the second side of a portion of theanode precursor after removal of the anode precursor from the sheet ofmaterial of FIG. 4F.

FIG. 4H illustrates a portion of an anode generated from the anodeprecursor of FIG. 4G.

FIG. 5A through FIG. 5D illustrate a first mask and a second masksuitable for use with a sheet of material from which an electrode isconstructed. FIG. 5A is a topview of the first mask.

FIG. 5B is a bottomview of the second mask.

FIG. 5C is a topview of the portion of the sheet of material thatincludes the first mask aligned with the second mask. In FIG. 5C, thefirst mask and the sheet of material are treated as transparent. As aresult, the features underlying the first mask are evident in FIG. 5C.

FIG. 5D is a magnified view of an edge of the first mask and the secondmask arranged as shown in FIG. 5C.

FIG. 6A through FIG. 6D illustrate a first mask and a second masksuitable for use with a sheet of material from which an electrode isconstructed. FIG. 6A is a topview of the first mask.

FIG. 6B is a bottomview of the second mask.

FIG. 6C is a topview of the portion of the sheet of material thatincludes the first mask aligned with the second mask. In FIG. 6C, thefirst mask and the sheet of material are treated as transparent. As aresult, the features underlying the first mask are evident in FIG. 6C.

FIG. 6D is a magnified view of an edge of the first mask and the secondmask arranged as shown in FIG. 6C.

FIG. 7 is a flow diagram for a process of recovering one or morechemicals from spent etching solution.

FIG. 8 illustrates a system that is suitable for recovering one or morechemicals from spent etching solution.

DESCRIPTION

A sheet of material is fabricated to include inactive regions that eachhas multiple projections extending from a perimeter of an imaginarycircle. The inactive regions are concentrically positioned on opposingsides of the sheet of material but are rotated relative to one another.A capacitor electrode is removed from the sheet of material such that apath along which the electrode is removed from the sheet of materialextends across the inactive regions. As a result, a fraction of eachinactive region on the sheet of material becomes an inactive region onthe resulting electrode. Electrical conductors can be connected to theinactive regions through techniques such as welding. The presence of theprojections on the inactive regions combined with the inactive regionsbeing rotated relative to one another on opposing sides of the sheet ofmaterial reduces strain near the interface between the inactive regionsand the active regions of the electrode. Accordingly, the configurationof the inactive regions on the electrode reduces the waviness andwarping of the electrode.

The active regions in the sheet of material can be formed by exposingthe active regions to an etching solution. The etching solution createstunnels or channels in the active regions on the sheet of material.Creating these tunnels causes metal ions from the sheet of material tobe present in the spent etching solution. One or more chemicalcomponents that were present in the etching solution can be recovered byadding a precipitant to the spent etching solution so as to form aprecipitation solution with a precipitate and a supernate. Theprecipitate includes a compound that includes the metal ions and thesupernate includes cations that are disassociated from the precipitant.The cations from the precipitant can be removed from the supernate andthe result can serve as a recovery solution. One or more adjustmentsolutions can then be added to the recovery solution so as to return atleast a portion of the chemical components to concentration levelswithin initial specifications for the etching solution. The adjustedsolution can then serve as a recovered etchant that can be mixed withfresh etching solution or can be used in place of fresh etchingsolution.

This approach to recovering chemical components from an etching solutionhas consistently yielded a recovered etchant where at least 30 wt % ofeach at least a portion the chemical components (one or more acids, oneor more oxidizers, and one or more surfactants) that were originallypresent in the etching solution are present in the recovered etchantand/or in the recovery solution. Accordingly, the recovery technique canhave a recovery rate that is greater than 30 wt % for all or a portionof the chemical components in the etching solution. Additionally, usingthe recovered etchant to generate anodes for a capacitor has yieldedanode with the same capacitance levels as unused etching solution.Further, an etching solutions that include sodium perchlorate in theacid etch solution at 3 to 4 w/w % can be used to create an anode with acapacitance above 1.25 microF/cm² at 490 Volts allowing a capacitor withan energy density above 5.5 J/cc and volume below 8 cc to be achieved.The inventors have not been able to re-create these performance levelswithout the use of sodium perchlorate. The ability to use the abovemethod to recover the sodium perchlorate greatly reduces the costs offabrication such a capacitor and can make commercialization practical.

FIG. 1A through FIG. 1H illustrate the construction of a capacitor. FIG.1A is a sideview of an anode 10 that is suitable for use in a capacitor.FIG. 1B is a cross-section of the anode 10 shown in FIG. 1A taken alongthe line labeled B in FIG. 1A. FIG. 1C is a cross-section of the anode10 shown in FIG. 1A taken along the line labeled C in FIG. 1A.

The anode 10 includes an active region 11 that includes, consists of, orconsists essentially of a layer of anode metal oxide 12 over a layer ofan anode metal 14. Suitable anode metals 14 include, but are not limitedto, aluminum, tantalum, magnesium, titanium, niobium, and zirconium. Asillustrated in FIG. 1B, in some instances, the anode metal oxide 12surrounds the anode metal 14 in that the anode metal oxide 12 ispositioned on both the edges and the faces of the anode metal 14. Manyanode metal oxides 12 can exist in more than one phase within the samematerial state (solid, liquid, gas, plasma). For instance, an anodemetal oxide 12 such as aluminum oxide can be in a boehmite phase(AlO(OH)) that is a solid or in alpha phase corundum oxide phase(α-Al₂O₃) that is also a solid.

The anode 10 also includes an inactive region 15 that includes, consistsof, or consists essentially of the layer of anode metal 14 may or maynot exclude the anode metal oxides 12. The inactive region is present ona first side and one a second side of the anode. The shape of theinactive region is not shown in detail in FIG. 1D. As will be describedin detail below, the shape of the inactive region is selected to reducewaviness of the anode. In some instance, the anode metal oxide 12 isformed on the anode metal by converting a portion of the anode metal tothe anode metal oxide 12 through oxidation of the anode metal oxide 12.In these instances, the active region of the anode may be thinner thanthe inactive region of the anode as is evident in FIG. 1C.

FIG. 1D is a sideview of a cathode 16 that is suitable for use in thecapacitor. FIG. 1E is a cross-section of the cathode 16 shown in FIG. 1Dtaken along the line labeled D in FIG. 1D. The cathode 16 includes alayer of cathode metal oxide 18 over a layer of a cathode metal 20.Suitable cathode metals 20 include, but are not limited to, aluminum,titanium, stainless steel. Although not illustrated, the cathode metalcan be layer of material on a substrate. For instance, the cathode metalcan be a titanium or titanium nitride coating on a substrate such as ametal and/or electrically conducting substrate. Examples of suitablesubstrates include, but are not limited to, aluminum, titanium, andstainless steel substrates. The cathode metal oxide 18 can be formed onthe cathode metal 20 by oxidizing the cathode metal 20 in air. Thecathode metal 20 can be the same as the anode metal 14 or different fromthe anode metal 14. In some instances, the cathode metal 20 and theanode metal 14 are both aluminum. As illustrated in FIG. 1E, in someinstances, the cathode metal oxide 18 surrounds the cathode metal 20.For instance, the cathode metal oxide 18 is positioned over the edgesand faces of the cathode metal 20. Although not illustrated in FIG. 1Dand FIG. 1E, the cathode can include an inactive region where thecathode metal 20 is exposed. One or more electrical conductors can beconnected to the exposed cathode metal using techniques such as welding.The electrical conductors can provide electrical communication betweenthe cathode and a terminal of the capacitor.

The anodes 10 and cathodes 16 are generally arranged in an electrodeassembly 22 where one or more anodes 10 are alternated with one or morecathodes 16. For instance, FIG. 1F is a cross section of an electrodeassembly 22 where anodes 10 are alternated with cathodes 16. The anodes10 and cathodes 16 can be constructed according to FIG. 1A through FIG.1E. A separator 24 is positioned between anodes 10 and cathodes 16 thatare adjacent to one another in the electrode assembly 22. The electrodeassembly 22 typically includes the anodes 10 and cathodes 16 arranged ina stack or in a jelly roll configuration. Accordingly, the cross sectionof FIG. 1F can be a cross section of an electrode assembly 22 havingmultiple anodes 10 and multiple cathodes 16 arranged in a stack.Alternately, the cross section of FIG. 1F can be created by winding oneor more anodes 10 together with one or more cathodes 16 in a jelly rollconfiguration. However, as the anodes become more brittle due toincreased surface area, it may not be practical or possible to form ajelly-roll configuration. Suitable separators 24 include, but are notlimited to, kraft paper, fabric gauze, and woven for non-woven textilesmade of one or a composite of several classes of nonconductive fiberssuch as aramids, polyolefins, polyamides, polytetrafluoroethylenes,polypropylenes, and glasses.

The electrode assembly 22 is included in a capacitor. For instance, FIG.1G is a schematic diagram of a capacitor that includes the electrodeassembly 22 of FIG. 1F positioned in a capacitor case 26. Although notillustrated, the one or more anodes in the electrode assembly 22 are inelectrical communication with a first terminal 28 that can be accessedfrom outside of the capacitor case 26. The one or more cathodes 16 inthe electrical assembly are in electrical communication with a secondterminal 30 that can be accessed from outside of the capacitor case 26.In some instances, the one or more anodes include or are connected toelectrical conductors such as tabs (not shown) that provide electricalcommunication between the one or more anodes and the first terminal 28and the one or more cathodes 16 include or are connected to electricalconductors such as tabs (not shown) that provide electricalcommunication between the one or more cathodes 16 and the secondterminal 30. The capacitor can include one or more electrical insulators(not shown) positioned as needed to prevent shorts-circuits within thecapacitor.

FIG. 1H is a sideview of an interface between an anode 10 and a cathode16 that are adjacent to one another in the capacitor of FIG. 1G. Theillustration in FIG. 1H is magnified so it shows features of the anode10 and cathode 16 that are not shown in FIG. 1A through FIG. 1F. In theactive region of the anode, the face of the anode 10 includes channels32 that extend into the anode metal 14 so as to increase the surfacearea of the anode metal 14. Although the channels 32 are shown extendingpart way into the anode metal, all or a portion of the channels 32 canextend through the anode metal. Suitable channels 32 include, but arenot limited to, pores, trenches, tunnels, recesses, and openings. Insome instances, the channels 32 are configured such that the anode has anumber of channels/area greater than or equal to 30 million tunnels/cm².Increasing the number of channels has been shown to increase thebrittleness of the anodes and/the sheet of material from which theanodes are extracted. Accordingly, increasing the surface area of theanode can result in a more brittle anode or sheet of material. In theactive region 11 of the anode, the anode metal oxide 12 is positioned onthe surface of the anode metal 14 and is positioned in the channels 32.The anode metal oxide 12 can fill the channels 32 and/or anode oxidechannels 34 can extend into the anode metal oxide 12. However, it isgenerally not desirable for the anode metal oxide 12 to fill thechannels 32 because filling the channels 32 can lead to reducedcapacitance and electrical porosity.

The inactive region 15 of the anode includes the anode metal 14.However, in the inactive region 15 of the anode, the anode excludes one,two, or three components selected from the group consisting of the anodemetal oxide 12, the channels 32 and the anode oxide channels 34. In theillustration of FIG. 1H, the inactive region of the anode excludes thechannels 32 and the anode oxide channels 34. Although an electricalconductor such as a tab can be attached to one or both sides of theanode, the electrical conductor is not shown in FIG. 1H in order tobetter illustrate the interface construction.

In FIG. 1H, an active region of a cathode is shown interfaced with aninactive region of the anode; however, an inactive region of the cathodecan be interfaced with the inactive region of the anode. The surface ofthe cathode 16 optionally includes cathode channels 36 that extend intothe anode metal 14 so as to increase the surface area of the anode metal14. Suitable cathode channels 36 include, but are not limited to, pores,trenches, tunnels, recesses, and openings. The cathode metal oxide 18can be positioned on the surface of the cathode metal 20. When thecathode metal 20 includes cathode channels 36, the cathode metal oxide18 can be positioned in the cathode channels 36. The cathode metal oxide18 can fill the cathode channels 36 and/or cathode oxide channels 38 canextend into the cathode metal oxide 18.

An electrolyte 40 is in contact with the separator 24, the anode 10 andthe cathode 16. The electrolyte 40 can be positioned in the cathodeoxide channels 38. When the cathode metal 20 includes cathode oxidechannels 38, the electrolyte 40 can be positioned in the cathode oxidechannels 38. The electrolyte 40 can be a liquid, solid, gel or othermedium and can be absorbed in the separator 24. The electrolyte 40 caninclude one or more salts dissolved in one or more solvents. Forinstance, the electrolyte 40 can be a mixture of a weak acid and a saltof a weak acid, preferably a salt of the weak acid employed, in apolyhydroxy alcohol solvent. The electrolytic or ion-producing componentof the electrolyte 40 is the salt that is dissolved in the solvent.

A capacitor constructed according to FIG. 1A through FIG. 1H can be anelectrolytic capacitor such as an aluminum electrolytic capacitor, atantalum electrolytic capacitor or a niobium electrolytic capacitor. Anelectrolytic capacitor is generally a polarized capacitor where theanode metal oxide 12 serves as the dielectric and the electrolyte 40effectively operates as the cathode 16.

FIG. 2A through FIG. 2H illustrate a method of generating an anode foruse in a capacitor constructed according to FIG. 1A through FIG. 1H. Asheet of material 48 can acquired either by fabrication or purchase froma supplier. As will be evident below, one or more anodes are constructedfrom the sheet of material 48. FIG. 2A is a topview of the sheet andshows a face of the sheet positioned between edges. One or more masks 49are positioned on the sheet of material 48 so as to protect the regionof the sheet of material 48 where an inactive region of an anode will bepositioned while leaving exposed the region(s) of the sheet of material48 where an inactive region of an anode will be positioned. As will bediscussed in more detail below, the masks 49 can be positioned onopposing sides of the sheet of material 48 and aligned with one another.Suitable masks 49 include, but are not limited to, inks, polymercoatings such as ink-jet applied curable polymers, photoresists and hardmasks such as oxides.

FIG. 2B is a portion of a cross section of the sheet showing aninterface between the face of the sheet of material 48 and theatmosphere 50 in which the sheet is positioned. The cross section istaken through the line labeled B in FIG. 2A. Accordingly, one of themasks 49 is shown on the side of the sheet illustrated in FIG. 1B. Thesheet of material 48 can include, consist of, or consist essentially ofthe anode metal 14.

A surface area enhancement phase can be performed so as to increase thesurface area of the exposed portions of the sheet of material 48. Forinstance, preliminary channels 52 can be formed in the sheet of material48 so as to provide the sheet of material 48 with the cross section ofFIG. 2C. As is evident from FIG. 2C, the mask 49 protects the underlyingsheet of material 48 from the formation of the preliminary channels 52.Suitable methods of forming the preliminary channels 52 include, but arenot limited to, laser removal and/or drilling, etching such as chemicaletching and electrochemical etching. In one example, the etching iselectrochemical etching or electrochemical drilling. In electrochemicaletching and/or electrochemical drilling, the sheet of material 48 is atleast partially immersed in a bath that includes, consists of, orconsists essentially of an etching solution such as an electrochemicaldrilling (ECD) solution initially having a pH of less than 5 or evenless than one while passing an electrical current through the sheet ofmaterial 48. Additional examples of suitable methods for forming thepreliminary channels 52 and/or additional details of suitable methods ofelectrochemical etching and/or electrochemical drilling can be found inU.S. patent application Ser. No. 11/972,792, filed on Jan. 11, 2008,granted U.S. Pat. No. 8,535,527, and entitled “Electrochemical DrillingSystem and Process for Improving Electrical Porosity of Etched AnodeFoil;” U.S. patent application Ser. No. 10/289,580, filed on Nov. 6,2002, granted U.S. Pat. No. 6,858,126, and entitled “High CapacitanceAnode and System and Method for Making Same;” and U.S. patentapplication Ser. No. 10/199,846, filed on Jul. 18, 2002, granted U.S.Pat. No. 6,802,954, and entitled “Creation of Porous Anode Foil by Meansof an Electrochemical Drilling Process;” each of which is incorporatedherein in its entirety.

In some instances, the surface area enhancement phase also includeswidening of the preliminary channels 52. Widening of the preliminarychannels can reduce or stop the anode metal oxide 12 from filling thechannels 32. For instance, the distance across the preliminary channels52 on the sheet of FIG. 2C can be increased to provide a sheet ofmaterial 48 having the channels 32 shown in the cross section of FIG.2D. In some instances, the preliminary channels 52 are formed andwidened so as to remove more than 52% or 60% of the sheet of material 48from the sheet of material 48 and/or to create more than 30 millionchannels/cm² of the sheet of material 48.

Suitable methods for widening the preliminary channels 52 include, butare not limited to, chemical and electrochemical processes. In oneexample of the widening process, widening of the preliminary channels 52includes immersing at least a portion of the sheet of material 48 in anelectrolyte solution that includes, consists of, or consists essentiallyof a chloride or nitrate. Additional examples of suitable methods forwidening of the preliminary channels 52 and/or additional details aboutthe above methods of widening preliminary channels 52 can be found inU.S. patent application Ser. No. 05/227,951, filed on Feb. 22, 1972,granted U.S. Pat. No. 3,779,877, and entitled “Electrolytic Etching ofAluminum Foil;” U.S. patent application Ser. No. 06/631,667, filed onJul. 16, 1984, granted U.S. Pat. No. 4,525,249, and entitled “Two StepElectro Chemical and Chemical Etch Process for High Volt Aluminum AnodeFoil;” U.S. patent application Ser. No. 11/972,792, filed on Jan. 11,2008, granted U.S. Pat. No. 8,535,527, and entitled “ElectrochemicalDrilling System and Process for Improving Electrical Porosity of EtchedAnode Foil;” U.S. patent application Ser. No. 10/289,580, filed on Nov.6, 2002, granted U.S. Pat. No. 6,858,126, and entitled “High CapacitanceAnode and System and Method for Making Same;” and U.S. patentapplication Ser. No. 10/199,846, filed on Jul. 18, 2002, granted U.S.Pat. No. 6,802,954, and entitled “Creation of Porous Anode Foil by Meansof an Electrochemical Drilling Process;” each of which is incorporatedherein in its entirety.

The mask(s) 49 can be removed after forming the preliminary channels 52in the sheet of material 48 or after widening of the preliminarychannels 52. FIG. 2D illustrates the mask(s) 49 removed after wideningof the preliminary channels 52; however, the mask(s) 49 can be removedafter forming the preliminary channels 52 in the sheet of material 48and before widening of the preliminary channels 52. After removing themask(s) 49 from the sheet of material 48, inactive region(s) 57 areformed on the sheet of material 48 as evident in FIG. 2D. The inactiveregion(s) 57 are located on the regions of the sheet of material 48where the masks were previously positioned.

The anode metal oxide 12 is formed on the anode metal 14 that is exposedin the exposed portion of the sheet of material 48. For instance, theanode metal oxide 12 can be formed on the anode metal 14 that is exposedin FIG. 2D so as to provide a sheet of material 48 according to FIG. 2E.The anode metal oxide 12 extends into the channels 32 so as to provideanode oxide channels 34. Forming the anode metal oxide 12 on the exposedanode metal 14 can include converting a portion of the existing anodemetal 14 to the anode metal oxide 12 or adding a layer of the anodemetal 14 over the previously existing anode metal 14. Converting aportion of the existing anode metal 14 to the anode metal oxide 12 caninclude reacting the anode metal 14 with a component such as oxygen. Theanode metal oxide 12 is formed so the anode metal oxide 12 is in a firstphase of the anode metal oxide 12. As an example, when the anode metal14 is aluminum, the boehmite phase (AlO(OH)) of aluminum oxide is formedas the anode metal oxide 12. The first phase of the anode metal oxide 12is desirable for the final capacitor. For instance, the first phase ofthe anode metal oxide 12 generally serves as the dielectric for thecapacitor.

An example of a suitable method of forming the anode metal oxide 12 onthe anode metal 14 includes an optional hydration layer formationoperation, one or more oxide formation operations, and one or morethermal treatments. In some instance, the hydration layer formationoperation is optionally performed before the one or more oxide formationoperations and the one or more oxide formation operations are performedbefore the one or more thermal treatments.

The hydration layer formation operation forms a hydration layer indirect contact with the exposed anode metal 14. The hydration layer caninclude, consist of, or consist essentially of the anode metal 14,hydrogen, and water. For instance, the hydration layer can include,consist of, or consist essentially of a hydrate of the anode metal 14.When the anode metal 14 is aluminum, the hydration layer can include,consist of, or consist essentially of aluminum hydrate.

In some instances, the hydration layer is formed on the anode metal 14by placing the sheet of material 48 in a bath liquid that includes,consists of, or consists essentially of water. In one example, the bathliquid is de-ionized water. The bath liquid may be held at a temperaturebetween 60° C. and 100° C. In some instances, the bath liquid ismaintained at about 95° C. The sheet of material 48 can remain in thebath liquid for a formation time. The formation time can be greater than1 minute and/or less than 20 minutes. The hydration can help form abetter quality oxide during the one or more oxide formation operations.

An example of a suitable oxide formation operation includes, but is notlimited to, mechanisms that convert existing anode metal 14 to anodemetal oxide 12 such as anodic oxidation. In anodic oxidation, the sheetof material 48 is placed in an electrolytic bath while a positivevoltage is applied to the sheet of material 48. The thickness of thelayer of anode metal oxide 12 can be increased by increasing the appliedvoltage. When the anode metal 14 is aluminum, anodic oxidation forms alayer of the boehmite phase (AlO(OH)) of aluminum oxide on a layer ofaluminum. In one example of anodic oxidation, the anode metal oxide 12is formed by placing the sheet of material in citric acid while apositive voltage of 400-550 volts is applied to the sheet of materialfor a period of time between 30 minutes to 150 minutes. Additionally oralternately, the electrical current that results from the appliedvoltage can be monitored and the sheet of material can be removed fromthe electrolytic solution in response to the electrical currentexceeding a treatment threshold.

The layer of oxide formed during the first oxide formation operationperformed on the sheet of material replaces and/or consumes thehydration layer formed during the hydration layer formation operation.As a result, the hydration layer is generally not present on the layerof material after the first oxide formation operation.

In some instances, the thermal treatments are each performed after anoxide formation operation. The thermal treatments elevate thetemperature of the sheet of material enough to drive out water from thelayer of anode metal oxide 12 formed during the previous oxide formationoperation(s). The removal of this water has been shown to decrease theleakage of capacitors. However, it is not desirable to remove all of thewater from the layer of anode metal oxide 12. Additionally, applyinghigh levels of thermal energy to the sheet of material can increase thelevel of deformation in a capacitor that includes an electrode made fromthe sheet of material. As a result, reducing the amount of thermalenergy applied to the sheet of material while removing this water maylead to both decreased leakage and decreased deformation.

A suitable thermal treatment includes one or more thermal compressionoperations. An example of a suitable thermal compression operation iscompressing the sheet of material between surfaces for a compressiontime with at least one of the surfaces having an elevated temperatureduring the compression.

FIG. 2F illustrates an example of a compression mechanism for performinga compression operation. The compression mechanism includes twocompression members. In FIG. 2F, a metal plate serves as each of thecompression members. Each of the compression members includes acompression surface that is in direct contact with the sheet of materialduring the compression operation. A contact portion of each compressionsurface is the portion of the surface that is in contact with the sheetof material during the compression operation. The location of thecontact portion on one of the compression members in diagram A of FIG.2F is illustrated by dashed lines.

As is evident from the arrow labeled C in FIG. 2F, the compressionmembers can be moved relative to one another. For instance, a first oneof the compression members can be immobilized while the secondcompression member is moved relative to the first compression member.Alternately, both of the compression members can be moved.

To prepare for the compression operation, the sheet of material isplaced between the compression members as shown in diagram A of FIG. 2F.The compression members are then moved relative to one another so thecontact portion of each compression surface is in direct physicalcontact with the sheet of material as shown in diagram B of FIG. 2F. Thecompression surfaces apply pressure to the sheet of material during thecompression operation. The compression operation continues for thecompression time that is desired for the compression operation. Afterthe compression time associated with the last compression operation isreached, the compression members can be moved apart and the sheet ofmaterial removed from between the compression members.

Although FIG. 2F shows the compression members as plates, thecompression members can be other components. For instance, one of thecompression members can be the side of an oven or the side of some otherstructure. Additionally or alternately, the compression members can bedifferent structures. For instance, one of the compression members canbe a plate as shown in FIG. 2F while another compression member is aside of an oven.

Although FIG. 2F shows the compression members as being independent ofone another, the compression members may be physically connected to oneanother. For instance, the compression members can be hinged or can bedifferent parts of a medium that is connected by a fold.

One or more of the compression members apply thermal energy to the sheetof material during a compression operation. For instance, the one ormore compression members can heat the sheet of material during acompression operation. As an example, the contact portion of one or moreof the compression surface can be at a compression temperature that isabove room temperature. One or more of the compression members caninclude a heating mechanism for bringing the contact portion of acompression surface to the desired compression temperature. Forinstance, a resistive heater can be mounted on a plate that serves as acompression member. Alternately, a plate that serves as a compressionmember can include one or more channels through which a heated fluid isflowed. In some instances, the heating mechanism for bringing one ormore of the compression surfaces to the desired compression temperaturecan be external to one or more of the compression members. For instance,the compression members can be located in an oven before and during thecompression treatment. As an example, the compression membersillustrated in FIG. 2F can be located in an oven before and during thecompression treatment. The oven can be maintained at the compressiontemperature in order to keep the temperature of the contact portion ofthe compression surfaces at the desired compression temperature.

Each of the compression operations in a thermal treatment is performedfor a compression time. The compression times associated with differentcompression operations can be the same or different. In some instances,the compression time is not long enough for the temperature of the sheetof material to reach the compression temperature. Accordingly, thetemperature of the sheet of material at the end of the compressionoperation (final operation temperature) can be different from thecompression temperature.

During a compression operation, a suitable pressure for applying to thesheet of material (compression pressure) is a pressure greater than 0.1once per square inch or 1 once per square inch and/or less than 1.0 psior 5.0 psi. During a compression operation, a suitable compressiontemperature for applying to the sheet of material is a temperaturegreater than 200° C., or 300° C., and/or less than 600° C., or 800° C.In some instances, the maximum temperature of the sheet of materialduring a compression operation is greater than 200° C., or 300° C.,and/or less than 600° C., or 800° C. Suitable compression times include,but are not limited to, compression times greater than 1 second, 5seconds and/or less than 10 seconds, 1 minute or ten minutes. In someinstances, the compression pressure and/or compression temperature areheld constant for the compression time during a compression operation.

In one example, a thermal treatment includes at least two compressionoperations performed at different pressure levels. A first one of thecompression operations can be a low pressure compression and a secondone of the compression operations can be a high pressure compression.The low pressure compression is performed at a lower compressionpressure than the high pressure compression. In some instances, the highpressure compression is performed immediately after the low pressurecompression without removing the sheet of material from between thecompression members and without other compression operations beingperformed between the low pressure compression and the high pressurecompression.

The low pressure compression can take advantage of the direct physicalcontact between the compression members and the sheet of material inorder to quickly elevate the temperature of the sheet of material towarda final operation temperature that is desired for the start of the highpressure compression. Suitable compression pressures for the lowpressure compression include, but are not limited to, pressures greaterthan 0.1 once per square inch or 1 once per square inch and/or less than0.1 psi or 0.5 psi. Suitable compression temperatures for the lowpressure compression include, but are not limited to, temperaturesgreater than 200° C., or 300° C., and/or less than 600° C., or 800° C.Suitable final operation temperatures for the low pressure compressioninclude, but are not limited to, temperatures greater than temperaturesgreater than 200° C., or 300° C., and/or less than 600° C., or 800° C.Suitable compression times for the low pressure compression include, butare not limited to, times greater than 1 second, 5 seconds and/or lessthan 10 seconds, 1 minute or ten minutes. In some instances, the sheetof material is at or near room temperature before the low pressurecompression. In some instances, the compression pressure and/orcompression temperature are held constant or substantially constant forthe compression time during the low pressure compression.

The high pressure compression can be performed for a duration thatdrives out the water from the layer of anode metal oxide 12 and/or thatcauses cracks to form in the anode metal oxide 12. Suitable compressionpressures for the high pressure compression include, but are not limitedto, pressures greater than 0.5 psi and/or less than 1.0 psi or 2.0 psi.Suitable compression temperatures for the high pressure compressioninclude, but are not limited to, temperatures greater than 200° C., or300° C., and/or less than 600° C., or 800° C. Suitable compression timesfor the high pressure compression include, but are not limited to, timesgreater than 1 second, 2 seconds and/or less than 10 seconds, 1 minuteor ten minutes. In some instances, the compression temperatures for thehigh pressure compression is the same as the compression temperature forthe low pressure compression. In some instances, the compressionpressure and/or compression temperature are held constant orsubstantially constant for the compression time during the low pressurecompression.

The increase in pressure between the low pressure compression and thehigh pressure compression can be done slowly. For instance, the increasein pressure can be at a rate greater than 0.0 psi/minute or 0.05 psi/minand/or less than 0.5 psi/min or 2 psi/min.

FIG. 2A through FIG. 2F illustrate a method of using fabrication toacquire a sheet of material 48 having an anode metal oxide 12 on ananode metal 14. Alternately, any stage of the sheet of material 48 shownin FIG. 2A through FIG. 2F can be acquired by purchase from a supplier.

One or more anode precursors 56 are extracted from the sheet of material48. Accordingly, a portion of the sheet of material 48 serves as theanode precursor 56. Suitable methods of removing an anode precursor 56from the sheet of material 48 include, but are not limited to cuttingthe anode precursor 56 out of the sheet of material 48. A suitablemethod of cutting the anode precursor 56 out of the sheet of material 48include mechanical cutting method such as die cutting where the anodeprecursor is punched or stamped from a sheet of material using amechanical die. Another suitable method of cutting the anode precursor56 out of the sheet of material 48 includes no-contact cutting methodssuch as laser cutting of the anode precursor 56. FIG. 2G illustrates useof a laser 58 to cut anode precursors 56 out of a sheet of material 48constructed according to FIG. 2F although other mechanisms for removingthe anode precursors 56 can be used.

The line along which an anode precursor 56 is removed from the sheet ofmaterial 48 (the separation line) is labeled P in FIG. 2G. Theseparation line passes through the inactive region(s) 57 of the sheet ofmaterial 48. As a result, the anode precursor 56 includes a portion ofthe inactive region(s) 57 of the sheet of material 48. At least aportion of the inactive region(s) 57 included on the anode precursors 56will become the inactive region 15 on the anode formed from the anodeprecursors 56.

The one or more anode precursors 56 constructed according to FIG. 2Athrough FIG. 2G are included in a capacitor precursor 61 according toFIG. 2H. For instance, one or more of the anode precursors 56 arecombined with one or more separators 24 and one or more cathodes 16 soas to form an electrode assembly 22 with the components arranged asdisclosed in the context of FIG. 1A through FIG. 1F. The electrodeassembly 22 is placed in a capacitor case 26 along with the electrolyte40. Any electrical connections needed for operation of the capacitorprecursor 61 are made and the capacitor case 26 is sealed.

The capacitor precursor 61 can optionally be put through an aging phase.The aging phase can be configured to form an anode metal oxide 12 on theedges on the one or more anode precursors 56 in the capacitor and/or onany other exposed anode metal 14. The aging process can use water in theelectrolyte 40 to form the oxide. The phase of the anode metal oxide 12formed during the aging phase is not necessarily the same as the firstphase of the anode metal oxide 12. For instance, when the anode metal 14is aluminum, the anode metal oxide 12 formed during the aging phase isnot the boehmite phase (AlO(OH)) but is similar. Suitable methods foraging the capacitor precursor 61 include, but are not limited to,holding the capacitor at an elevated temperature while charged. Forinstance, in some instances, aging includes holding the capacitor at atemperature greater than 50° C. or 70° C. and/or less than 100° C. or200° C. for a time greater than 2 hours, or 20 hours, and/or less than50 hours or one hundred hours while charged to a voltage greater than 50V, or 200 V and/or less than 600 V or 800 V. In one example, agingincludes holding the capacitor at about 85° C. for 24 to 36 hours whilecharged to about 400 V.

The capacitor precursor 61 can optionally be put through a testingphase. The testing phase can be configured to test the capacitorprecursor 61 for charge and discharge functionality. Completion of thetesting phase can provide the anode and capacitor of FIG. 1A throughFIG. 1H. Accordingly, the capacitor is ready for use in the desiredapplication and/or for resale.

The construction and arrangement of the masks 49 are not shown in detailin the method of FIG. 2A through FIG. 2H. FIG. 3 is a cross section of aportion of the sheet of material 48 after formation of the preliminarychannels 52 and before removal of the masks 49. A first one of the masks49 is positioned on a first side 60 of the sheet of material 48 and asecond one of the masks 49 is positioned on a second side 62 of thesheet of material 48. The masks are aligned with one another on theopposing sides of the sheet of material 48. For instance, an imaginaryline labeled C in FIG. 3 can be perpendicular to the first side or thesecond side can extend through a center of the first mask 64 and thesecond mask 66. The center can be the centroid.

The shape of the first mask 64 and the second mask 66 is selected toreduce strain at the interface between the active region and theinactive region of an electrode such as an anode. FIG. 4A through FIG.4D illustrate a first mask 64 and a second mask 66 suitable for use withthe sheet of material 48. FIG. 4A is a topview of the first mask 64 andFIG. 4B is a bottomview of the second mask. FIG. 4C is a topview ofportion of the sheet of material 48 that includes the first mask 64aligned with the second mask 66. In FIG. 4C, the first mask 64 and thesheet of material 48 are treated as transparent. As a result, thefeatures underlying the first mask 64 are evident in FIG. 4C. The sheetof material 48 shown in FIG. 4C can be before or after fabrication ofone, two, or three components selected from the group consisting of theanode metal oxide, the channels and the anode oxide channels. FIG. 4D isa magnified view of an edge of the first mask 64 and the second mask 66arranged as shown in FIG. 4C. The vertical lines shown on the first mask64 and horizontal lines shown on the second mask 66 of FIG. 4A throughFIG. 4D are provided for the purposes of showing relative orientation ofthe first mask 64 and the second mask 66 and do not represent physicalfeatures on the first mask 64 and the second mask 66. FIG. 4E is amagnified view of a first mask 64 and a second mask 66. Although thefirst mask 64 and the second mask 66 of FIG. 4E are not aligned, theyeach have the same angular orientation as shown in FIG. 4C and FIG. 4D.

The first mask 64 and the second mask 66 include projections extendinginwards or outwards from an imaginary circle shown by the dashed circlesin FIG. 4E. The first mask 64 and the second mask 66 of FIG. 4A throughFIG. 4E are shown extending outwards from a circle. Each of theprojections contacts the circle twice. In FIG. 4A through FIG. 4E, thecircle is tangent to the perimeter of the mask 49. However, as will beshown below, the circle can pass through vertices on the perimeter ofthe mask 49. Accordingly, the projections can be constructed such thatthe circle is tangent to a projection at two locations, pass through avertex at two locations, or is tangent to a projection at one locationand passes through a vertex at another location.

The projections in the first mask 64 are each associated with aprojection index labeled i=1 through N, the index increases withincreasing angle, and the projection with index i=1 straddles ororiginates at the angle θ=0°. The value of N can be a function of circlediameter or circumference. For instance, a circle with a circumferenceof 10 mm can have N=20. Examples of suitable values of N include valuesgreater than or equal to 3 or 4 and/or less than 40, or even 100. Eachprojection i intersects the circle twice: once at an angle θ_(i); andagain at an angle θ_(i′). In some instances, the projections are spacedapart on the circle and the angular separation between adjacentprojections can be called θ_(i,s) (not shown) where θ_(i,s) indicatesany angular separation between projection i and projection 1+1. In otherinstances, the projections are adjacent to one another without beingspaced apart as shown in FIG. 4A through FIG. 4E. In these instances,θ_(i′)=θ_(i+1). The angular range of the circle that each projectionoccupies is θ_(i,R). The angular range can be determined as an absolutevalue of the difference between the angles where projection i intersectsthe circle. For instance, the angular range can be determined fromθ_(i,R)=|θ_(i)−θ_(i′)|. The projections can be periodically arrangedaround the circle. For instance, each projection can have the sameshape, the angular range (θ_(i,R)) is the same for each projection i,and the angular separation (θ_(i, s)) is the same for each projection i.In another example, each projection has the same shape, the angularrange (θ_(i,R)) is the same for each projection i, and the angularseparation is 0.0° for each projection i. When the projections have aperiodic arrangement, the projections have an angular period ofP=θ_(i,R)+θ_(i,s).

The projections in the second mask 66 are each associated with aprojection index labeled j=1 through M, the index increases withincreasing angle. The value of M can be a function of circle diameter orcircumference. For instance, a circle with a circumference of 10 mm canhave M=20. Examples of suitable values of M include values greater thanor equal to 3 or 4 and/or less than 40, or even 100. Each projection jintersects the circle twice: once at an angle θ_(j); and again at anangle θ_(j′). In some instances, the projections are spaced apart on thecircle and the angular separation between adjacent projections can becalled θ_(j,s)(not shown) where θ_(j,s) indicates any angular separationbetween projection j and projection j+1. In other instances, theprojections are adjacent to one another without being spaced apart asshown in FIG. 4A through FIG. 4E. In these instances, θ_(j)=θ_(j+1). Theangular range of the circle that each projection occupies is θ_(j,R).The angular range can be determined as an absolute value of thedifference between the angles where projection i intersects the circle.For instance, the angular range can be determined fromθ_(j,R)=|θ_(j)−θ_(j′)|. The projections can be periodically arrangedaround the circle. For instance, each projection can have the same shapeand size, the angular range (θ_(j,R)) is the same for each projection j,and the angular separation (θ_(j,s)) is the same for each projection j.In another example, each projection has the same shape and size, theangular range (θ_(j,R)) is the same for each projection j, and theangular separation is 0.0° for each projection j. When the projectionshave a periodic arrangement, the projection have an angular period ofP=θ_(j,R)+θ_(j,s).

In some instances, the second mask 66 has the same size and shape as thefirst mask 64. For instance, each projection i and j can have the sameshape and size, the angular ranges (θ_(j,R) and θ_(j,R)) can be the same(θ_(R)) for all values of i and j and the angular separations (θ_(j,s)and θ_(i,s)) is the same (θ_(S)) for each projection i and j. In anotherexample, each projection i and j has the same shape and size, theangular ranges (θ_(j,R) and θ_(j,R)) are the same for all values of iand j and the angular separations (θ_(j,s) and θ_(i,s)) is 0.0° for eachprojection i and j.

The second mask 66 can be rotated relative to the first mask 64 by aconstant value. For instance, the second mask can be arranged such thatθ_(j)=θ_(i)+c° and θ_(j)=θ_(i′)+c° where c° is a constant. In FIG. 4Cand FIG. 4D, the second mask 66 is rotated relative to the first mask 64by one half the period. For instance, c°=P/2, or c°=(θ_(R)+θ_(S))/2, orc°=(θ_(R))/2 when θ_(S)=0.0°.

In FIG. 4E, the circle has a radius labeled r in FIG. 4E and theamplitude of the projections is labeled c₃. In some instances, theradius is greater than 0.05 inches, 0.125 inches and/or less than 0.25inches or 1 inch and/or the amplitude of the projections is greater than1%, or 5% and/or less than 7.5% or 50% of the diameter.

FIG. 4F illustrates a portion of a first side of the sheet of material48 and the corresponding portion from the second side of the sheet ofmaterial 48. The first mask and the second mask have been removed fromthe sheet of material 48 exposing an inactive region 57 on the firstside and on the second side of the sheet of material 48. As discussedabove, the inactive region 57 excludes one, two, or three componentsselected from the group consisting of the anode metal oxide 12, thechannels 32 and the anode oxide channels 34. In contrast, the regions ofthe sheet of material 48 that contact the inactive regions include thechannels 32, anode oxide channels 34, and anode metal oxide 12 on thesheet of material 48 discussed above in the context of FIG. 2A throughFIG. 2H. The channels and anode oxide channels are not shown in FIG. 4F.The shape and orientation of the first mask and the second mask inactiveregions 57 is transferred to the inactive regions 57. Accordingly, theinactive regions 57 can each include projections extending from a circleas disclosed in the context of the first mask and the second mask.

The path along which an anode precursors 56 is removed from the sheet ofmaterial 48 (the separation path) is labeled P on the first side 60 andthe second side 62 of the sheet of material 48 shown in FIG. 4F. Theseparation line passes through the inactive regions 57 of the sheet ofmaterial 48.

FIG. 4G shows the first side 60 and the second side 62 of a portion ofthe anode precursor 56 after removal of the anode precursor from thesheet of material 48. The anode precursor 56 includes a portion of theinactive regions 57 from the sheet of material 48. Because theseparation line extended through the inactive regions 57, a portion ofeach inactive region 57 is maintained on the anode precursor 56. Forinstance, the portion of inactive regions 57 on the anode precursor 56includes one, two, three, four, or more projections and zero to twopartial projections extending from a semicircle rather than the circledisclosed above. Additionally, the one or more projections extend from asemicircle (labeled S in FIG. 4G) that can be a portion of the circlefrom which the projections previously extended. The separation path canbe selected such that a perimeter of the semicircle on the anodeprecursor includes more than 30%, or 50% and/or less than 90%, or 100%of the circumference of the imaginary circle from the sheet of material48.

As is evident from a comparison of FIG. 4F and FIG. 4G, a portion of theinactive region 57 is not retained on the anode precursor 56. Forinstance, the portion of the inactive region 57 labeled SC in FIG. 4F isnot included in the anode precursor 56. As a result, this portion of theinactive region does not actually need to be fabricated on the sheet ofmaterial 48. As a result, the masks 49 (first mask 64 and second mask66) and/or the inactive region 57 on the sheet of material can includeone, two, three, four, or more projections and zero to two partialprojections extending from a semicircle rather than the circle andassociated projections disclosed above.

FIG. 4H illustrates a portion of an anode 10 generated from the anodeprecursor 56 of FIG. 4G. The portion of the inactive region 57 includedon the anode precursor 56 becomes the inactive region 15 on the anode.An electrical conductor such as a tab 70 is connected to the inactiveregion 15 on the anode by a technique such as welding. The inactiveregion 15 can have a surface area sized such that the welding processremoves the anode metal oxide 12 from all or a portion of the inactiveregion 15. As a result, all or a portion of the inactive region 15 caninclude the anode metal oxide 12 or all or a portion of the inactiveregion 15 can exclude the anode metal oxide 12. For the purposes ofillustration, FIG. 4F through FIG. 4H illustrate the inactive region 15without the anode metal oxide 12. The resulting anode is suitable foruse in the fabrication of an electrode assembly, capacitor precursor,and capacitor.

As noted above, the projections can be periodically arranged around thecircle and accordingly around the resulting semicircle. In someinstances, this can be represented using simple mathematical equations.For instance, using polar coordinates (p, θ), a suitable perimeters forthe first mask and the second mask can be represented by p=r+c₃ cos(c₁θ+c₂) where p represents the perimeter of the first mask 64 and/orthe second mask 66, c₂ represents a constant that is greater than orequal to 0° and less than or equal to 360°, c₃ represents the amplitudeof the projections, and c₁ represents a positive or negative integerthat is not equal to zero. The constant c₂ represents the angularrotation of the perimeter. Accordingly, in order to provide the desiredrotation of the first mask 64 relative to the second mask, the value ofc₂ can be different for the first mask 64 and the second mask 66. Insome instances, the values of r, c₃, and c₁ are c₂ are the same for thefirst mask 64 and the second mask 66 but the value of c₂ is differentfor the first mask 64 and the second mask 66.

FIG. 4A through FIG. 4H illustrate an example of the projection shapewhere the perimeter of each projection is curved. FIG. 4A through FIG.4H illustrate an example of the projection shape where the perimeter ofeach projection is curved. However, the perimeter of each projection caninclude one or more straight segments and/or one or more curvedsegments. FIG. 5A through FIG. 5D illustrate an example of a first mask64 and a second mask 66 each the perimeter of each projection includesonly straight segments. FIG. 5A is a topview of the first mask 64 andFIG. 5B is a bottomview of the second mask. FIG. 5C is a topview ofportion of the sheet of material 48 that includes the first mask 64aligned with the second mask 66. In FIG. 5C, the first mask 64 and thesheet of material 48 are treated as transparent. As a result, thefeatures underlying the first mask 64 are evident in FIG. 5C. FIG. 5D isa magnified view of an edge of the first mask 64 and the second mask 66arranged as shown in FIG. 5C.

FIG. 6A through FIG. 6D illustrate an example of a first mask 64 and asecond mask 66 each the perimeter of each projection includes a straightsegment and a curved segment. FIG. 6A is a topview of the first mask 64and FIG. 6B is a bottomview of the second mask. FIG. 6C is a topview ofportion of the sheet of material 48 that includes the first mask 64aligned with the second mask 66. In FIG. 5C, the first mask 64 and thesheet of material 48 are treated as transparent. As a result, thefeatures underlying the first mask 64 are evident in FIG. 6C. FIG. 6D isa magnified view of an edge of the first mask 64 and the second mask 66arranged as shown in FIG. 6C.

As is evident from FIG. 4A through FIG. 4G, the projections can besymmetrical around a line that is perpendicular to the circle orsemicircle. Alternately, as is evident from FIG. 5A through FIG. 6D, theprojections can be asymmetrical around a line that is perpendicular tothe circle or semicircle.

In some instances, the first mask 64 are second mask 66 are arrangedsuch that the orientation of the projections in the first mask 64 arereversed relative to the orientation of the projections in the firstmask 64. For instance, when looking at the sheet of material from asingle side, the second mask 66 can be a mirror image of the first mask64 but with the second mask 66 rotated relative to the first mask 64 asdisclosed above and as shown in FIG. 5A through FIG. 6D. Accordingly,the second mask and can have the same shape as the first mask, but canbe a mirror image of the first mask when looking at the sheet ofmaterial from a single side, and can be rotated relative to the firstmask 64 as disclosed above and as shown in FIG. 5A through FIG. 6D.Alternately, the first mask 64 and the second mask 66 are arranged suchthat the orientation of the projections have the same orientationrelative to one another as shown in FIG. 4A through FIG. 4G.

In some instances, the rotation of the second mask is such that segmentsof the first mask 64 align with segments of the second mask 66. Forinstance, linear segments on the mask of FIG. 5A and FIG. 5B becomealigned as shown in FIG. 5C and FIG. 5D. As an example, the linearsegments that are circled in FIG. 5A and FIG. 5B are aligned on thesheet of material 46 shown in FIG. 5C in that one of the segments ispositioned directly over the aligned segment on the sheet of material.As a result, a line can be drawn perpendicular to a face of the sheet ofmaterial and through the aligned segments for a continuous length of thesegments. These features of the first mask 64 and the second mask 66transfer to the inactive regions that result from the first mask 64 andthe second mask 66. This alignment of segments on the resulting inactiveregion(s) can enhance the degree of strain relief provided by theinactive regions.

Removal of the first mask 64 and the second mask 66 from the sheet ofmaterial causes the features attributed the shape, size, geometry andorientations of the first mask 64 and/or the second mask 66 to betransferred or substantially transferred to the resulting inactiveregions on the sheet of material and/or on the electrode. In someinstances, a substantial transfer of the features occurs as a result ofundercutting that occurs during etching. Accordingly, the description ofthe shape, size, geometry and orientation of the first mask 64 and thesecond mask 66 also apply to the inactive regions formed on the sheet ofmaterial and to at least a portion of each of the resulting inactiveregions on the electrode.

The sequence of events disclosed above for forming an anode and/or acapacitor can be performed in a sequence other than the disclosedsequence. For instance, the aging phase can be performed after thetesting phase.

Although the above methods of forming an anode have been disclosed inthe context of a capacitor, the above methods of forming anode to thefabrication of anodes, cathodes, positive electrodes, and/or negativeelectrodes in other energy storage devices such as batteries.

FIG. 7 is a flow diagram for a process of recovering one or morechemicals from spent etching solution. At process block 100, a sheet ofmaterial in which the preliminary channels 52 are to be formed is placedin a bath of etching solution. The sheet of material typically includes,consists essentially of, or consists of a metal such as aluminum. Insome instances, the etching solution includes or consists of one, two,three, or four chemical components selected from a group consisting ofacids, oxidizers, and surfactants. When forming tunnels in a sheet ofmaterial that includes or consists of aluminum, an example of a suitableetching solution for forming tunnels includes or consists ofhydrochloric acid and sulfuric acid as acids, sodium perchlorate as anoxidizer, and potassium perfluorobutane sulfonic acid (KFBS) as asurfactant.

The etching solution contains the chemical components at concentrationsthat fall within an initial component specification. The initialcomponent specification can specify concentrations of all or a portionof the chemical components in the component specification. Examples ofconcentrations include, but are not limited to, molar concentrations,weight concentrations, weight percentages, molar percentages, and ppm.As an example, an initial component specification for an etchingsolution that includes or consists of hydrochloric acid, sulfuric acid,sodium perchlorate, and potassium perfluorobutane sulfonic acid (KFBS)call for hydrochloric acid in a range of 0.60 to 0.80 wt %, sulfuricacid in a range of 0.80 to 1.0 wt %, sodium perchlorate in a range of3.0 to 4.0 wt %, and potassium perfluorobutane sulfonic acid (KFBS) in arange of 0 to 100 ppm with the remainder as water such as deionizedwater or tap water.

After the etching solution is contacted with the sheet of material, thespent etching solution includes dissolved metal ions from the sheet ofmetal. As a result, the spent etching solution includes or consists ofone, two, three, four, or five chemical components selected from a groupconsisting of acids, oxidizers, surfactants, and dissolved metal ionsfrom the sheet of material. For instance, when the sheet of material isaluminum, the spent etching solution can include one or more acids, anoxidizer, an optional surfactant, and dissolved aluminum ions. In oneexample, the spent etching solution includes hydrochloric acid andsulfuric acid as acids, sodium perchlorate as an oxidizer, potassiumperfluorobutane sulfonic acid (KFBS) as a surfactant, and dissolvedaluminum ions. In some instances, the spent etching solution has a pHlevel higher than 0.1 and/or less than 1.5 or 3.

At process block 102, the spent etching solution is mixed with aprecipitant so to form a precipitation solution where a precipitatecomes out of solution. The precipitant is selected such that theprecipitate is a compound that includes the metal ions from the sheet ofmaterial. In some instances, the precipitate is a crystal structure thatincludes the metal ions.

In some instances, the precipitant is a solid or liquid base that isadded to the precipitation solution so as to raise the pH of theprecipitation solution at a level where the solubility of theprecipitate in the precipitation solution drops to below the saturationlevel of the precipitate in the precipitation solution. The reducedsolubility causes the precipitate to come out of the precipitationsolution. Additionally, the precipitant can be selected such that whenthe precipitant is in the precipitation solution, the precipitant isdisassociated into ions that include a precipitant anion and aprecipitant cation. The precipitate can include the metal ions from thesheet of material and the precipitant anion and the precipitant cationscan remain in the supernate.

As an example, when the spent etching solution includes aluminumcations, the precipitant can be sodium hydroxide (NaOH), a base thatdissociates into sodium cations and hydroxide anions in water. Variousphases of aluminum hydroxide such as (Al(OH)₃) and aluminum hydratebecomes less soluble in the precipitation solution at pH levels greaterthan 5.5 and less than 8.0. As a result, the sodium hydroxide can beadded to the precipitation solution to increase the pH of theprecipitation solution and cause aluminum hydroxide to precipitate fromthe precipitation solution. For instance, the sodium hydroxide (NaOH)can be added to the precipitation solution at levels that maintain thepH of the precipitation solution at pH levels greater than 5.5 and lessthan 8.0. In some instances, the precipitant is selected such that theprecipitant cation is a base cation such as K⁺, Ca²⁺, Mg²⁺, and Na⁺.Examples of suitable precipitants include, but are not limited to, NaOH,KOH, Ca(OH)₂, and Mg(OH)₂. In some instances, the precipitant isselected such that the precipitant cation is also present in the etchingsolution before the addition of the precipitant in order to keep theprecipitant compatable with the etching solution. For instance, theexample etching solution set forth above includes Na⁺ from the sodiumperchlorate. When NaOH is used as the precipitant with this etchingsolution, the Na⁺ precipitant cation is already present in the etchingsolution.

At process block 104, the precipitate is settled out of theprecipitation solution. The combination of process block 102 and processblock 104 results in mixing of the precipitation solution for a mixingperiod followed by settling of the precipitation solution for a settlingperiod. The mixing period and the settling period can have an inverserelationship. For instance, increasing mixing periods can reduce theneeded settling period. Suitable mixing periods include, but are notlimited to, mixing periods greater than 1 hour or 7 hours and/or lessthan 48 hours. Suitable settling periods include, but are not limitedto, settling periods greater than 24 hours and/or less than 72 hours, or120 hours. In some instances, a ratio of the settling period to themixing period is greater than 4:1, and/or less than 120:1.

The precipitate can be separated from the supernate. The separation canbe concurrent with the settling of the precipitate or done after thesettling of the precipitate. The precipitate can be disposed of, orstored for later disposal. Alternately, one or more metal ion tests canoptionally be performed on a sample of the supernate before separatingthe precipitate and the supernate. The one or more metal ion tests canoptionally be performed so as to determine if the metal ions have beenremoved from the supernate. Examples of suitable metal ion testsinclude, but are not limited to, colorimetry, mass spectrometry, andatomic absorption. When the one or more metal ion tests indicate thatthe concentration of the metal ion in the supernate is at or above anupper concentration threshold, the settling period can be extended orthe precipitate and/or superanate can be discarded. When the settlingperiod is extended, the one or more metal ion tests can optionally beperformed again during and/or after the extended settling period so asto determine if the metal ions have been removed from the supernate.

When the one or more metal ion tests indicate that the concentration ofthe metal ion is supernate is below the upper concentration threshold,the precipitate is separated from the supernate. In some instances, theupper concentration threshold is greater than 0.1 mg/L and/or less than2.0 mg/L.

At process block 106, one or more additional refining steps canoptionally be performed on the supernate so as to further remove anyadditional particles from the sheet of material and/or precipitate fromthe supernate. For instance, the supernate can be filtered and/ordecanted so as to generate a refined supernate. The refined supernatecan serve as the supernate for the purposes of the following discussion.As will be discussed below, the refined supernate can be passed throughan ion exchange resin. The one or more refining steps can be selected toremove particles from the sheet of material and/or precipitate with asize that is sufficient to clog the ion exchange resin. In someinstances, the one or more refining steps are selected to removeparticles with diameters of at least larger than 0.5 microns.

The precipitant cation is removed from the supernate so as to provide arecovery solution (process block 108). Suitable methods for removing theprecipitant cation include, but are not limited to, ion exchangeoperations such as cation exchange. In some instances, the precipitantcation in the supernate is replaced with another cation such as hydrogencations (H⁺). The removal of the precipitant cation can reduce the pH ofthe supernate by more than 1, 2, or 4 scales of pH. In some instance,the precipitant cation is removed from the supernate so as to provide arecovery solution with a pH less than 1.0.

Suitable cation exchange mechanisms include, but are not limited to,resin beds. The resin can include active sites that exchange a hydrogencations (H⁺) for the precipitant cation (Na⁺ in the case of a NaOHprecipitant). In some instance, the resin includes plastic beads orplastic microbeads such as AMBERLITE-FPC23-H. The recovery solutionincludes the acids that were originally present in the etching solutionas a result of the exchange between the hydrogen cations (H⁺) for theprecipitant cation. For instance, when the etching solution includeshydrochloric acid (HCl), the addition of precipitant such as NaOH to theetching solution effectively converts the hydrochloric acid (HCl) tosodium chloride and the subsequent exchange of the sodium cations forthe hydrogen cations (H⁺) returns the sodium chloride to hydrochloricacid (HCl). Accordingly, the recovery solution includes the chemicalcomponents that were originally present in the etching solution. Forinstance, when the etching solution includes one or more acids, anoxidizer, the optional surfactant, the recovery solution includes theone or more acids, an oxidizer, and the optional surfactant when thesurfactant was present in the etching solution. As an example, therecovery solution includes hydrochloric acid and sulfuric acid as acids,sodium perchlorate as an oxidizer, and potassium perfluorobutanesulfonic acid (KFBS) as a surfactant when the etching solution includesthese components.

When a cation exchange process is used to remove the precipitantcations, the cation exchange resin can be refreshed. For instance, aregeneration solution can be flowed through the cation exchange resin soas to replace the precipitant cation at the active sites of the cationexchange resin with the hydrogen cations. In some instances, theregeneration solution includes an acid such as sulfuric acid. The resinbed can be refluidized to reduce compaction of the resin beforeintroduction of the regeneration solution.

The spent regeneration solution can be analyzed one or more times todetermine when the regeneration process is complete. For instance, theconcentration of ions in the spent regeneration solution can be measuredto determine when the regeneration solution starts to egress from theresin beds. Many factors such as flow rate, regeneration solutionconcentration, type of regeneration solution, direction of flow andregeneration time can contribute to the regeneration completeness.Suitable methods for analyzing the regeneration solution include, butare not limited to, titration. Regeneration can be considered to becomplete when the concentration of ions in the spent regenerationsolution falls below an ion concentration threshold. In some instances,the ion concentration threshold is chosen to indicate that insignificantamounts of ions remain to be exchanged by H+ ions in the exchange resinbeds. Suitable ion concentration thresholds include, but are not limitedto, ion concentration threshold less than 2 wt % and/or a change inconcentration over time less than 0.15 wt %. As an example, a suitableNa+ ion concentration threshold includes, but is not limited to, an ionconcentration threshold less than 2 wt % or a change in concentrationover time less than 0.15 wt %

Although it is possible for the concentrations of each chemicalcomponent in the recovery solution to be within the initial chemicalspecifications, the concentrations of one or more of the chemicalcomponents in the recovery solution (the recovered etchant componentconcentrations) will generally be outside of the initial chemicalspecifications. For instance, methods of removing the precipitantcation, such as cation exchange, generally output the differentcomponents at different times and/or over different durations in theprecipitant cation removal process. As a result, the recovery solutioncomponent concentrations will generally be outside of the initialcomponent specification. In some instances, the recovery solution outputfrom the ion exchanger can be periodically sampled and the samplesanalyzed to determine whether the chemical components are being outputfrom the ion exchanger in the desired ratios. Suitable methods foranalyzing the samples of the recovery solution include, but are notlimited to, titration. In some instances, the titration is thermometrictitration that measures the temperature change in the titration solutionto determine a reaction endpoint. The reaction endpoint indicates theconcentration of each chemical component such as the concentration ofhydrochloric acid, sulfuric acid or sodium perchlorate. An example of asuitable thermometric titration includes, but is not limited to, theASTM D664-11A test method.

The recovery solution can be treated so as to return the concentrationsof at least a portion of the chemical components in the recoverysolution to the initial component specification at process block 110.For instance, one or more adjustments solutions can be added to therecovery solution so as to generate an adjusted solution where theconcentrations of measured chemical components approach the initialcomponent specifications. The one or more adjustment solutions can beconfigured such that each adjustments solution includes a different oneof the measured chemical components. As a result, the chemicalcomponents can be independently added to the recovery solution.Alternately, one or more adjustment solutions can include more than oneof the chemical components that are added to the recovery solution.

Returning the recovery solution to the initial component specificationcan include one or more adjustment measurements where the concentrationsof at least a portion of the chemical components in the recoverysolution are measured. The portion of the chemical components that aremeasured during the adjustment measurements are the measured chemicalcomponents. The one or more adjustment solutions can be added to therecovery solution or the adjusted solution in response to the adjustmentmeasurements. For instance, when the first adjustment measurementindicates that the concentration of a particular one of the chemicalcomponents in the recovered etchant is below the initial componentspecification for that chemical component, additional amounts of theidentified chemical component can be added to the recovery solution byadding one or more of the adjustment solutions to the recovery solution.The addition of an adjustment solution to the recovery solution resultsin the formation of the adjustment solution. Additionally oralternately, when an adjustment measurement indicates that theconcentration of a particular one of the chemical components (theidentified chemical component) in the recovered etchant is above theinitial component specification for the identified chemical component,additional amounts of one or more of the chemical components that arenot the identified chemical component can be added to the recoverysolution so as to reduce the concentration of the identified chemicalcomponent in the resulting adjusted solution. After adding additionalamount(s) of one or more chemical components to the recovery solution,the process of sampling the recovery solution, performing an adjustmentmeasurement, and adding chemical component to the resulting adjustedsolution can be repeated until an adjustment measurement indicates thateach of the measured chemical components falls within the initialcomponent specification. As a result, the process of returning therecovery solution to the initial component specification can includegenerating a series of adjusted solutions. An adjusted solution havingeach of the measured chemical components fall within the initialcomponent specification can serve as the recovered etchant. Suitablemethods for the adjustment measurements include, but are not limited to,titration. In some instances, the titration is thermometric titration.

The inventors have surprisingly found that one or more of the chemicalcomponents in the etching solution need not be quantified in order toreturn the recovery solution to the initial component specification. Asa result, the adjustment measurements need not quantify the amount ofthe one or more excluded chemical components called the unmeasuredchemical components. As an example, when the etching solution includeshydrochloric acid, sulfuric acid, sodium perchlorate, and potassiumperfluorobutane sulfonic acid (KFBS), the amount of KFBS in the recoverysolution and/or recovered etchant need not be quantified by any of themeasurements. In this example, the amount of KFBS is added to therecovery solution in proportion to the other components. For instance,the amount of KFBS is added to the recovery solution in an amount thatwould bring the level of KFBS in the total volume of the added solutionsto the desired level and/or the level in the initial componentspecification.

When the first adjustment measurement taken on the recovery solutionindicates that each of the measured chemical components falls within theinitial component specification, the recovery solution can serve as therecovered etchant without adding any of the one or more adjustmentsolutions to the recovery solution.

Adding the one or more adjustment solutions to the recovery solution asdescribed above causes the concentration of the measured chemicalcomponents in the adjusted solution(s) and in the resulting recoveredetchant, to approach the concentration of the same chemical componentsin the etching solution. For instance, one, more than one, a portion, orall of the measured chemical component in the recovered etchant can eachhave a concentration that is within the concentration of that componentin the etching solution +/− an adjustment factor where the adjustmentfactor is less than or equal to 2 wt % or 0.5 wt % of the concentrationof that chemical component in the etching solution. In one example, theadjustment factor is 0.2 wt % of the concentration of the chemicalcomponents in the etching solution.

The recovered etchant can be mixed with the etching solution and theresult used to etch other capacitor electrodes, can be stored, and/orused to etch other capacitor electrodes without being mixed with theetching solution. The method of FIG. 7 has been shown to result in morethan more than 30 wt %, 50 wt % and less than 60 wt %, or 80 wt % of thechemical components that was included in the etching solution beingincluded in the recovered etchant. In view of these results, a firstetching solution can be used to etch a first sheet of material so as togenerate a spent etchant as described above. At least one chemicalcomponent can be recovered from the spent etchant. A second etchingsolution that includes at least one of the recovered chemical componentscan then be used to etch a second sheet of material as described above.Capacitors can be fabricated with electrodes that include the etchedfirst sheet of material second sheet and/or the etched second sheet ofmaterial.

FIG. 8 illustrates a system that is suitable for recovering one or morechemicals from spent etching solution. The system includes an etchantreservoir 120 that holds the etchant 122. Suitable reservoirs include,but are not limited to, a tank. The etchant is transported from theetchant reservoir to a bath reservoir 124 that holds the bath of theetching solution where the preliminary channels are etched in the sheetof material (not shown). The spent etchant 126 is generated from etchingthe preliminary channels in the sheet of material.

The spent etchant 126 is transported from the bath reservoir to a mixingreservoir 128 along with a precipitant 130. The mixing reservoir 128 isconfigured to provide mechanical mixing of the precipitant 130 and thespent etchant 126 so as to form a precipitation solution 132. Suitablemixing reservoirs include, but are not limited to, tanks. In someinstances, a suitable mixing tank is configured to remove a portion ofthe tank contents from at or near the bottom of the mixing tank and thenreturn the removed portion to the mixing tank contents at anotherlocation. The precipitation solution 132 is transported from the mixingreservoir 128 to a settling reservoir 136 where the precipitate 138 issettled from the supernate 140. Suitable settling reservoirs include,but are not limited to, tanks.

In some instances, the system includes multiple settling reservoirs 136because the settling period can be substantially larger than the mixingperiod. For instance, when precipitation solutions are mixed atdifferent times, it is possible that different mixed precipitationsolutions are being settled concurrently. The presence of multiplesettling reservoirs allows different precipitation solutions to betransported into different settling reservoirs. This arrangement canresult in different settling reservoirs concurrently holdingprecipitation solutions that were prepared at different times.

The system can optionally include a waste storage vessel 142. Theprecipitate from the settling reservoirs can be transported to the wastestorage vessel 142 for later treatment and/or disposal at anon-hazardous waste landfill.

As noted above, during or after settling, one or more metal ion testscan optionally be performed on a sample of the supernate so as todetermine if the metal ions have been removed from the supernate. Asample of the supernate for testing can be accessed from one or more ofthe settling reservoirs. When the one or more metal ion tests indicatethat the concentration of the metal ion in the supernate is below anupper concentration threshold, the supernate 140 is transported from theone or more settling reservoirs 136 to the one or more refiningcomponents 144. Examples of suitable refining components 144 include,but are not limited to, filtration systems. Suitable filtration systemsinclude, but are not limited to, filter arrays.

The system includes one or more precipitant cation removal components150. The refined supernate 146 is transported from the one or morerefining components 144 to the one or more precipitant cation removalcomponents 150. The precipitant cation removal components 150 are eachconfigured to remove the precipitant cation from the refined supernateso as to generate a recovery solution 152. Suitable precipitant cationremoval components include, but are not limited to, ion exchangesystems.

The system can include one or more adjustment reservoirs 154. Therecovery solution 152 is transported from the one or more precipitantcation removal components 150 to the one or more adjustment reservoirs154. One or more adjustments solutions 156 are added to the recoverysolution 152 held by the one or more adjustment reservoirs 154 so as togenerate a recovered etchant 158 having chemical componentconcentrations adjusted to the initial component specifications.Suitable adjustment reservoirs 154 include, but are not limited to,tanks.

As noted above, the one or more adjustment solutions 156 can be added tothe recovery solution in response to measurements where theconcentration of one or more chemical components in the recoverysolution and/or in the recovered etchant are measured. A sample(s) ofthe recovery solution 152 and/or the recovered etchant 158 for measuringthe component concentration(s) can be accessed from a sample valve in arecirculation loop in adjustment reservoirs 154.

The system can optionally include one or more storage reservoirs 160.The recovered etchant 158 can be transported from the one or moreadjustment reservoirs 154 to the one or more storage reservoirs 160where the recovered etchant can be stored. Suitable storage reservoirs160 include, but are not limited to, tanks. In addition or as analternative to storing the recovered etchant in the one or more storagereservoirs, the recovered etchant 158 can be transported from the one ormore storage reservoirs 160 and/or from the one or more adjustmentreservoirs 154 to the etchant reservoir 120. Accordingly, the recoveredetchant 158 can be mixed with fresh etchant.

When the one or more precipitant cation removal components 150 includean ion exchange system, the system can optionally include a regenerationreservoir 162 where the regeneration solution 164 is stored. After usingthe ion exchange system to remove precipitant cation from the refinedsupernate, the regeneration solution can be flowed through the ionexchange resin so as to prepare the ion exchange resin for removal ofthe precipitant cation from another refined supernate. The regenerationsolution that exits from the ion exchange system serves as spentregeneration solution 166. As noted above, in some instances, the spentregeneration solution 166 can be analyzed one or more times to determinewhen the regeneration process is complete. The spent regenerationsolution can be neutralized and/or transported from the one or moreprecipitant cation removal components to a wastewater system.

The above system discloses solutions being transported from onecomponent to another. The various components included in the system canoptionally be in liquid communication with one another. As a result, allor a portion of the disclosed transportations can be done by way ofpipes and conduits. The transportation through these mechanisms can bedriven by the use of pumps, gravity, and valves.

Example 1

Preliminary channels were electrochemically etched into an aluminumsheet of material using an etchant that included 0.70 wt % hydrochloricacid, 0.91 wt % sulfuric acid, 3.8 wt % sodium perchlorate, and 60 ppmpotassium perfluorobutane sulfonic acid (KFBS). Forming the preliminarychannels resulted in spent etchant with a pH of 0.5.

2170 gallons of the spent etchant was transported into a mixingreservoir along with 530 gallons of treated etchant sent as purgesolution and 46 gallons of NaOH so as to form a precipitation solutionthat was mixed for 22.5 hours. The resulting precipitation solution wastransported to a settling reservoir where the precipitation solutionremained for 4 days and 19.5 hours. During settling, a precipitate thatincluded Al(OH)₃ and a supernate formed in the mixing reservoir at avolume ratio of about 1:3.

A sample of the supernate was decanted by 0.45 micron single-usefiltering apparatus. A metal ion test performed on the refined supernateshowed a concentration of aluminum ions of 0.012 mg/L, which was belowthe upper concentration threshold of 0.5 mg/L.

The supernate was decanted by inline filtration. The decanted supernatewas filtered using a pleated polypropylene filter cartridge with a poresize of 0.5 micron to generate a refined supernate.

A cation exchange system was used to replace the sodium cations in therefined supernate with hydrogen cations (H⁺). The cation exchange systemincluded a bed of a cation exchange resin that was Amberlite FPC23H. Thecation exchange system had a downward flow design and the refinedsupernate was flowed through the bed of a cation exchange resin at arate of 17 gallons per minute. The recovery solution output from thecation exchanger was sampled at a period of 1350 gallons and the samplesanalyzed by thermometric titration. The titration showed that therecovery solution included 0.64 wt % hydrochloric acid, 0.94 wt %sulfuric acid, 3.8 wt % sodium perchlorate.

The precipitate sludge was transported from the settling tank to a wastestorage vessel for later disposal at a non-hazardous waste landfill.

After outputting the recovery solution, the refined supernate thatremained in the bed of cation exchange resin was pushed back to themixing reservoir at the beginning of the process using city water atapproximately 20 gallons per minute. The bed of cation exchange resinwas fluidized by city water. Regeneration of the cation exchange resinwas performed in two stages in order to prepare the bed for the nextrefined supernate. First, a regeneration solution of 5.3 wt % SulfuricAcid was downward flowed through the bed of a cation exchange resin at arate of 12 gallons per minute for 104 minutes. A second regenerationstage used 5.7 wt % Sulfuric Acid solution downward flow through half ofthe cation exchange resin at a rate of 14 gallons per minute for 80minutes.

The recovery solution was sampled and an adjustment determinationanalysis performed on the sample using mass balance calculation. Theadjustment determination analysis showed that the theoretical recoverysolution was 0.70 wt % hydrochloric acid, 0.91 wt % sulfuric acid, 3.75wt % sodium perchlorate, and 60 ppm potassium perfluorobutane sulfonicacid (KFBS). In response, 12.6 liters of 32% hydrochloric acid, 5.6liters of 60% sodium perchlorate, 39.6 gallons of city water and 3.9liters of KFBS were added to the recovery solution. The recoverysolution was sampled again and a second adjustment determination was notrequired. The adjustment measurement showed recovered etchant componentratios of 0.70 wt % hydrochloric acid, 0.91 wt % sulfuric acid, 3.8 wt %sodium perchlorate, and 60 ppm (KFBS). Since these recovered etchantcomponent ratios fell within the initial component specification, theresult was treated as recovered etchant.

The recovered etchant included 91 wt % of the hydrochloric acid that wasoriginally present in the etching solution, 100 wt % of the sulfuricacid that was originally present in the etching solution, 100 wt % ofthe sodium perchlorate that was originally present in the etchingsolution, and 100 wt % of the potassium perfluorobutane sulfonic acid(KFBS) that was originally present in the etching solution.

The recovered etchant was used as an etching solution to etch channelsin an aluminum foil that served as the sheet of material disclosedabove. The conditions under where the channels were etched in thealuminum foil were 120 seconds etch with 7 minutes of widening. Theetched aluminum foil was then formed. Anodes were cut from the resultand an electrolytic capacitor constructed with a volume of 8 cc. Theelectrolytic capacitor was tested and showed an energy density above 5.5J/cc with the anodes each showing a capacitance above 1.25 microF/cm² at490 Volts.

Other embodiments, combinations and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

1. A method of fabricating a capacitor, comprising: using a firstetching solution to etch a first sheet of material so as to generate aspent etchant; recovering at least one chemical component from the spentetchant; and using a second etching solution to etch a second sheet ofmaterial, the second etchant including the chemical component that wasrecovered from the spent etchant.
 2. The method of claim 1, furthercomprising: fabricating a capacitor with an electrode that includes aportion of the first sheet of material.
 3. The method of claim 1,wherein the recovered chemical component includes sodium perchlorate. 4.The method of claim 1, wherein the spent etching solution that includesmetal ions from the first sheet of material; and wherein recovering theat least one chemical component includes adding a precipitant to thespent etching solution so as to cause precipitation of a compound in aprecipitation solution, the compound including the metal ions from thesheet of material.
 5. A method of fabricating a capacitor electrode,comprising: exposing a sheet of material to an etching solution so as togenerate a spent etching solution that includes metal ions from thesheet of material; adding a precipitant to the spent etching solution soas to cause precipitation of a compound in a precipitation solution, thecompound including the metal ions from the sheet of material, theprecipitant being disassociated in the precipitation solution such thatthe precipitation solution includes cations from the precipitant; andremoving from the precipitation solution at least a portion of thecations from the precipitant.
 6. The method of claim 5, wherein theetching solution includes sodium perchlorate.
 7. The method of claim 5,wherein the etching solution includes one or more acids, one or moreoxidizers, and one or more surfactants.
 8. The method of claim 5,wherein the etching solution includes hydrochloric acid, sulfuric acid,sodium perchlorate, and potassium perfluorobutane sulfonic acid (KFBS).9. The method of claim 5, wherein the sheet of material includesaluminum and the spent etching solution includes aluminum ions.
 10. Themethod of claim 5, wherein removing the cations from the precipitationsolution includes performing a cation exchange on the precipitationsolution.
 11. The method of claim 5, wherein the precipitant is a base.12. The method of claim 5, wherein the cations from the precipitant area base cation.
 13. The method of claim 5, wherein adding the precipitantto the spent etching solution increases a pH of the precipitationsolution above the pH of the spent etching solution.
 14. The method ofclaim 5, wherein the precipitant is added to the spent etching solutionso as to maintain a pH of the precipitation solution in a range of 5.5to 7.0 during the precipitation of the compound.
 15. The method of claim5, wherein the etching solution includes one or more chemical componentsselected from a group consisting of one or more acids, one or moreoxidizers, and one or more surfactants; and the cations are removed fromthe precipitation solution so as to generate a recovery solution, amolar amount of each one of one or more of the chemical components inthe recovery solution being more than 30 wt % of the chemical componentsthat were originally included in the etching solution and are not water.16. The method of claim 5, wherein the etching solution includes one ormore chemical components selected from a group consisting of one or moreacids, one or more oxidizers, and one or more surfactants; and thecations are removed from the precipitation solution so as to generate arecovery solution; and one or more adjustment solutions are added to therecovery solution so as to generate a recovered etchant that includes atleast a portion of the chemical components at a concentration that iswithin the concentration of that component in the etching solution+/−0.5 wt %.
 17. The method of claim 12, wherein the one or morechemical components include hydrochloric acid, sulfuric acid, sodiumperchlorate, and potassium perfluorobutane sulfonic acid (KFBS).
 18. Themethod of claim 12, wherein the one or more chemical components includesodium perchlorate and the recovered etchant includes the sodiumperchlorate at a concentration that is within the concentration of thesodium perchlorate in the etching solution +/−2 wt %.